Prime (rank)

When a new Matrix-Bearer is chosen, if the a Transformer has affinity for the Matrix, he may be transformed into a super-powerful Prime.

Primes are appointed for life, serving until either their deactivation of choosing to step down.

Not all Matrix-Bearers are Primes. Conversely, most Primes are Autobot leaders, because the Matrix is generally only bestowed on leaders.

Japanese equivilant: Convoy

[Note: Not all Convoys are Primes. If you can lead ants to a picnic, you're a Convoy in Japan.]

From Teletraan I: The Transformers Wiki, a Wikia wiki.